E46 M3 rotors

I have a few questions about the E46 M3 rotors.
1. Why does the European E46 M3 have cross-drilled rotors and the US M3 have plain rotors?
2. Will cross-drilled rotors provide improved braking?
3. Will the European cross-drilled rotors fit on the US M3?
4. Will I need to replace any additional parts or hardware other than pads if I get the cross-drilled rotors?
Thank you, G.S.
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I think they're the same fitment but check on m3forum.net I can only imagine that it's for cost cutting because they see the US as being the market for looks over performance.
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wrote:

I think they're the same fitment but check on m3forum.net I can only imagine that it's for cost cutting because they see the US as being the market for looks over performance.
<JS> If that was the case, drilled and slotted rotors look Way Cool, and USA models would all have them at any cost.
PS I bought slotted and drilled rotors for an E36, and the extra machine work was only $20 over plain rotors. That works out to $5 per rotor, hardly a number that would keep them out of the market.
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Jeff,
Thanks for pointing me to m3forum.net.
One poster there said the following about the rotor differences between Europe and US:
*************************************************************** 1) Fear of how easy it is to sue a manufacturer here for product liability. BMW's lawyers were nervous about possible liability concerns. They were worried that some owners would use the cross-drilled rotors too long (well past their wear thickness rating) increasing the possibility of the rotor cracking between the holes. That could potentially lead to the very remote possibility of catastrophic brake failure. (and the subsequent lawsuits blaming BMW for this) The poor maintenance reputation we have in the U.S. (at not being diligent about performing routine inspections on our cars) is something I heard before from other manufacturers as well. It seems we are somewhat 'marked' in that regard.
2) Cost - Euro-spec rotors have a two-piece 'floating' construction that is more expensive to manufacture. The aluminum hat (instead of CAST IRON) uses steel pins to mate to the outer cast iron friction ring. This type of rotor effectively doubles the manufacturing cost per rotor, so a cheaper but still effective alternative was selected. (100% CAST IRON solid rotor) Also, U.S.-spec M3's had the lowest base price point of any E46 M3 in the world. Our U.S.-spec E46 M3's are at least $10,000USD cheaper than any other world market. That significantly reduces the profit margins on those cars. Volume sales only cover a part of that deficit. You have to remove some standard equipment (making them optional), and manipulate a few other things in order to make the much cheaper base price financially feasible.
3) Noise - The cross drilled rotors make a distinct noise as the air passes through the cooling vanes and the cross drilled holes at lower speeds. They also create a sound based on how the edges of the brake pads interact with the edges of the drilled holes. This noise is very irritating to some individuals, and it was determined that the solid rotors would not produce this noise problem. ***************************************************************
What was said in item 1 & 3 seems reasonable. What was said in item 2 about cost is anybody's guess.
G.S.
On Tue, 12 Feb 2008 16:45:29 GMT, "Jeff Strickland"

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I did not point you anywhere.
I do not know the validity of any of the three points you made, except that Point # 3 is 100% true, the slots and drill holes make lots of noise -- they click under light braking at low to moderate speeds. They could make noise at other times too, but I have them mounted on a convertible that has lots of other noise that drowns out the brakes. I do not find the clicking to be annoying or harmful, but it is noticible noise.
wrote:

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Just that euro M3 rotors aren't slotted - only drilled. I don't notice any brake noise other than when completely standing on the brakes and then the noise is usually "whaaaaaaaa!"
I think list price of euro rotors is in excess of $300 each.
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adder1969 wrote:

You've actually stood on your brakes? I have a Toyota Supra TT, which also has some pretty massive brakes, and I don't think I ever have. I'm afraid I'd go through the windshield. 8)
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I don't know.

Have you ever had brake fade? If you have had issues with brake fade, cross-drilling will provide improved cooling that will reduce the problems.
I have never encountered brake fade on any modern car. If you are driving on a racetrack, or regularly do high speed mountain driving, though, brake fade could be a problem for you.

I believe so. There are also plenty of third-party racing rotors that are available.

No. However, you should know that there are rotors out here that are optimized for long life, and there are rotors that are optimized for low fade under racing conditions. In addition, some rotors are much quieter than others. In general (and I don't know if this is the case for the BMW OEM ones), long life and high performance don't go together. You can buy plenty of third-party rotors from the racing equipment suppliers, some of which have better cooling than any of the stock ones, at the expense of life.
If you have never encountered brake fade and never had to pull over and see your rotors glowing, there is no reason to use anything but the OEM stock ones.
On the other hand, a stock Plymouth Valiant in San Francisco will suffer from brake fade just in normal driving... --scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

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